Fabricating magnesium



Patented Sept. 20, 1932 UNITED STAJFES- PA'lizVr.l oel-*ICE JOHN E. HOY, or MIDLAND, MICHIGAN, iissrcrironl To rms: now cia-Entrant coMPANY,`

or MIDLAND, MrcHIGAN, n coRronA'rIoN or MICHIGAN' .v

FABRICATING MAGNESIUM Application :tiled May 29, 1928. Serial No. 281,548.

ture is imparted to the metal characterized by elongating the grains in the direction of the longitudinal axis, such structure possessing great strength and rigidity and being adapted to withstand relatively great stresses, more especially when said stresses are so applied that the major component thereof is in a longitudinal direction with reference to the member stressed. A further object is to produce, as a new' article of manufacture, an improved metallic airplane propeller, or like mechanical element',N possessing the aforesaid structure, which by reason of its lighter weight and great strength has an important advantage over other types of metallic propellers now in `common use. Other objects and advantages will appear from thedescription as hereinafter setforth. To the accomplishment of the foregoing and related ends, said invention, then, consists of the features hereinafter fully described and particularly pointed out in the claims.

The annexed drawing and the following description set forth in detail but one of the various ways in which the principle of the invention may be employed.

In said annexed drawing:

Fig. 1 is a perspective view of a cast billet of a magnesium alloy; Fig. 2 is a central vertical section through an extrusion die illustrating the cast billet in the process of being extruded; Fig. 3 is an end elevation 'of an `extruded billet; Fig. 4 is a central vertical 'section through a hammer or press forge; Fi, 5 is a section on line 5-5 of Fig. 4; and ig.' y6l is a plan view taken from above of the lower die block of the forge il- ""lustrated in Fig. 4.;

' It is known that magnesium can be extruded :withiiia temperature range of 650 to sono F. '(U. s.A 1,570,868, Temp1in),and further that magnesium base alloys can ber mechanically worked by forging or similar methods at temperatures between 500 and 700 F. (U. S. 1,374,960, Veazey). Still further it has been stated that forging can be successfully accomplished at somewhathigher temperatures up to 788 to 800 F. or above. (Cf. Ind. & lEng. IChem. 19: 1199, Oct. 1927). It has not hitherto been pointed out, however, that by combining the operations of extrusion and forging, or comy pressing, in successive steps a greater improvement isy imparted to the structure and physical properties of magnesium-base alloys than is obtained by means of either operation alone. v

For example, an alloy well adapted to undergo improvement by means of the aforesaid operations has the composition: Copper 4 per cent., aluminum 2 per cent., cadmium 2 per cent., manganese 0.20 per cent., magnesium 91.80 per cent. The following table gives the tensile strength and elongation for said alloy, in the extruded, forged and both extruded and forged forms, respectively Tensile strength, Per cent lbs. ppt `elongation Extruded 36,850 6. 0 Forum 39, 000 7. 0 Forged and extruded 40, 490 8.5

It will be seen that the greatest strength much greater strength and durability. A disadvantage of lsuch metallic propellers is that they are much heavierthan wood p-ropellers, and this excessive vweight entails a corresponding sacrifice in the xusefull'oad which c the plane is able to carry., Owing to the fact that magnesium-base alloys possess a lower specific gravity than the commercial aluminum alloys, in general weighing only. twothirds as much as the aluminumalloys, their use for propellers effects an important advantage in the saving of weight "of an airplane. 1

In'carrying out my process I start with a cast ingot of magnesium or magnesium-base alloy, one illustrative example of which has hereinbefore been given. There is, however, a wide range of composition within which magnesium-base alloys are capable of undef?? going improvement according to my process, and such compositions may include other metals as minor constituents, instead of or loy7 is used herein, in the ,sense well underin addition to those in such example. I, therefore, do not limit myself tothe aforementioned alloy, which is chosen only by way ofillustration, but wish it understood that I mayguse any suitable magnesiumbase alloy which in general will contain from 85 to 90 per cen-t., or more, of magnesium. The tern11nology any sultable magneslum' base alstood by those skilled in the art of plastic deformation of magnesium alloys, to cover var-lons magnesium base alloys, the exact composition of which depends both upon the nature of the compression steps and upon the alloying ingredients to be used. .The exact percentage of the vingredients to be used is chosen so. that all of the constituents of the alloy, When in. condition for compression, will have melting points above the temperatureseniployed in the compression steps. The

addition of relatively large amounts of al-' \loying ingredients, as is well understood,

usually decreases the ease of plastic deformation ofthe alloy, although a higher percentl` .age of alloying ingredients may be-present when the alloy is to be compressed by operations such as press forging or rolling than when the alloy is to be compressed byhammer forging. For instance, inthemagnesium-alu-` minum series, heat treated alloys containing 6 per cent or less of aluminum are best adapted for hammer forging, while those containing 10 per cent or less of aluminum may be press forged o'r rolled. In like manner, in

lustrated as having a diamond or grid shape for easier formation ofa propeller, whereby it undergoes a reduction in cross-section of approxlmately 50,per cent. The extruded billet 2 thereupon subjected to further heat treatment for four hours at 750 to 850 F.,

in order substantially to remove any strains that may have been set up due to the extrusion.` The billet is lthen forged, either by a hammer orpress 11 and 12, into approximately itslinalform, starting at a temperature between 800o and 880F. In so doing, the metal. is drawn out longitudinally in order to increase the Aeffective 'workingV in such direction as originally produced in Lthe extrusionl operation, ands thereupon shaped to the form of the propeller blade, orother mechanical part, which is to be fashioned. It is then finished by machining according to the'usual methods.

As worked according to the several steps herein described, thegrain structure of the metal is caused to assume a characteristic elongated form, which imparts the valuableI and improved properties claimed in my process. proved procedure is illustrated 1n the annexed drawing, of which Fig. l isa perspec- The formation of an article by my imf slightly smaller diameter than the bore 7 .l

End blocks 9 and 10 prevent displacement of the extrusion die 6 and assist in absorbing 'most' of the load imposed upon the extrusion die by the ram. It is,- of course, to be understood that the extruded billet 2 may have any particular cross section as long as this cross section is a uniform area throughout the longitudinal extent of the billet. As illustrated herein, the extruded billet is given a grid shape in order that a propeller may be more easily fashioned.- However, it is tobe understood that the shape may vary with the particular article to be manufactured.

In Fig. 4 the step of forging is illustrated as taking place between an upper die block and a lower die block 12, which may have complimental recesses, one of which, 13, is shown in Fig. 6. The forging operation causesthe extruded billet 2 to assume approximately the nal form of propeller having a body portion 3, a hub 14 and a small projection 15. As understood by those skilled in the art, the projection 15 has the function of providing a gripping end for operatwell known to those versed in the science of metallography, a greater degree of grain refinement in a metal almost invariably predicates -a correspondingly greater degree of strength in the absence of other deciding factors. In the case in hand, such elongated structure and greater refinement of grain 1s directly the Iresult of themethod of working disclosed.4

While I have described my invention in terms of making a product having an elon-v gated grain structure (based on the specific working o f the alloy cited and the appearance of its microstructure), I do not wish to be limited to that exact description since obviously the production of the improved article is the important thing regardless of any statement as to exactly what happens during its production.

Obviously my `process is equally adapted to the'manufacture of other articles as well as airplane propellers, wherein equivalent properties are to be obtained, such as, for example, a connecting rod for an internal combustion engine, and I wish to include within the scope of my invention any such further applications, structures, structural members or parts made from magnesium or magnesium-base alloys in so far as their fabrication shall involve the steps herein described.

IOther modes of applying the principle of -my inventionmay be employed instead of the ing in general one explained, change being made as regards the means and the steps herein disclosed, provided those stated by any of the following claims or their equivalent be employed.

In the following claims, it is understood that magnesium yincludes any magnesiumbase alloy of the character described, containper cent. or more of magnesium.

I therefore particularly point out and distinctly claim as my invention:-

1. In a method of fabricating articles of:

magnesium, the steps which consist in casting a billet of said metal, then extruding said billet to form a billet o-f uniform cross sectional area, then working and shaping 'i said billet into approximately its final form by compression.

2. In a methodof fabricating articles of magnesium, the steps which consist in casting a billet of said metal, then extruding said billet to form a billet of uniform cross tudinal axis of said billet, then working andshaping said.billet into approximately its nal form by forging to further elongate a billet of said metal, then extruding said billet to form a billet of uniform cross sectional area, then working and shaping said billet into' approximately its final form by compression, said extrusion and compression steps being performed at a. temperature between 7 50 and 900 F., and said billet being subjected to heat treatment previously to leac-h step.

5. In a method of fabricating articles of magnesium, the st'epswhich consist in casting a billet of said metal, then extruding said billet to form a billet of uniform cro-ss sectional area, whereby the grain structure is elongated in the direction of the longitudinal axis of said billet,.then working and shaping saidbillet into approximately its final form by forging to further elongate such grain structure in the same direction,

saidextrusion and forging steps being performed at a temperature between 750 and 900 F., and said billet being subjected to heat treatment previously to each step.

6. In'a method of manufacturing a mag-` nesium propeller, the steps which comprise heat treating a billet of said metal, then extruding said billet to a billet having a uniform cross sectional area, then forging said billettoapproximately its final shape, and then machining it.

7. In the method of manufacturing a magnesium propeller, the steps which comprise heat treating a billet of said metal, then extruding said' billet to a billet having a uniform cross sectional area, then forging said billet to approximately its final shape and finally machining said billet, said forging step being controlled to accentuate the elongated grain structure produced by the 'extruding step.

form crosssectional area, thenV further working and shaping said extruded billet to approximately its nal form by compression.

9. In the method of manufacturing a magnesium propeller, the steps which comprise heat treating a billet of said metal, then extruding said billet to a billet having al uniform cross sectional area, then forging said billet to approximately its final shape.

10. In the method of making a, propeller, the steps which' comprise extruding a magnesium billet to a billet of uniform cross sectional area at a temperature between 750 5 and 900 F., and then further working and shaping said extruded billet to approximately its linal form by compression and at a like temperature.

11. In a method of making a propeller, the

steps which comprise extruding a previously iheat treated billet of magnesium to a billet of uniform cross sectional area at a temperature between about 750 and 900 F., eat treating the same, and then further Working and shaping said ,billet into approximately its final form by compression and at a like temperature.

12. In a method of making a propeller, the steps Which comprise extruding a previouslyY heat treated billet of magnesium to a billet of uniform cross sectional area at a temperature between labout 750 and 900 F., heat treating the same, and then further Working and shaping said billet, by forging -it into approximately its final form and at a like temperature.

lSigned by me this 24th day of May, 1928.

JOHN E. HOY. 

